Spectacular Motion of a Single Electron Caught on Video

What does an electron look like? Is it round, is it a cube, or what? So far, no one has been able to see an electron directly, because photons from a beam of light directed at the electron alter the position of the electron, so they can't bounce back into the eye to form an image.

The electron is a fundamental subatomic particle that carries a negative electric charge, with a mass that is one billionth of a billionth of a billionth of a gram. Now, a team of scientists caught the motion of a single electron on video, for the first time.

Humphrey Maris, a professor of physics at Brown University and Wei Guo, a doctoral student at the same institution, were able to observe a strange, scattered point of light moving down the screen, through liquid helium.

The electron sometimes followed a straight line and sometimes a snakelike path and the simple fact it can be seen is a spectacular achievement for the two physicists.

"We were astonished when we first saw an electron moving across the screen," said Maris"Once we had the idea, setting it up was surprisingly easy."

The footage was done using a home camera and the two researchers took advantage of the fact that bubbles form around electrons in supercold liquid helium and used sound to make the bubbles expand and light to see them.

Bubbles are created by the electron repelling nearby atoms and are actually small spherical spaces around the electron itself. Since electrons can't be observed directly in experimental applications, observing the bubble is the closest thing.

Usually, these bubbles are shrunk and destroyed by the surface tension of the liquid, but superfluid helium has very little surface tension, so the bubble can become much larger. The two opposing forces balance when the diameter of the bubble is about 40 angstroms - still far too tiny to see.

The expanding bubbles produced around 2,000 photons that formed a series of electron-bubble images on each frame of videotape.